Laser scanner shadowing
Sadly you cannot isolate the effects of a lamp on an object in Cycles as you can using Blender Internal Renderer layers.

So I tried building an intense isolated lamp &amp; enclosure. From this I include a volume box for the emitted light to excite. The enclosure cam be hidden from the camera by simply turning off its Object Properties > Cycles Settings > Ray Visibility > Camera.



The material for the volume uses a scatter with a density of 0.03
While the Spot lamp in the box with a slit has a high emit/strength value of 50,000. You can have a wide spread or a narrow beam by altering the Spot angle.

To reduce render time you could build the volume box to exactly match the beam spread of the laser.